Incandescent light bulbs are a source of electric light that creates light by running electricity through a resistive filament, thereby heating the filament to a very high temperature, so that it glows and produces visible light. Incandescent bulbs are made in a wide range of sizes and voltages, from 1.5 volts to about 300 volts. The bulbs consist of a generally glass or plastic enclosure with a filament of tungsten wire inside the bulb through which an electrical current is passed. Incandescent lamps are designed as direct “plug-in” components that mate with a lamp socket via a threaded Edison base connector (sometimes referred to as an “Edison base” in the context of an incandescent light bulb), a bayonet-type base connector (i.e., bayonet base in the case of an incandescent light bulb), or other standard base connector to receive standard electrical power (e.g., 120 volts A.C., 60 Hz in the United States, or 230V A.C., 50 Hz in Europe, or 12 or 24 or other D.C. voltage). The base provides electrical connections to the filament. Usually a stem or glass mount anchors to the base, allowing the electrical contacts to run through the envelope without gas/air leaks.
With reference to FIG. 1, a typical incandescent candle bulb is displayed. The envelope 11 generally comprises glass, although other light transmissive material may be used. The envelope 11 encloses a tungsten filament 13, through which an electrical current is passed. The base 15 includes two metal contacts 16, 18 that are attached to the filament. Two stiff wires 17, 19 are mechanically supporting the filament 13. When the bulb is hooked up to a power supply, an electrical current flows from one contact to the other, through the wires 16, 18 and the filament 13. A candle bulb is similar in function and general shape to other incandescent bulbs, but is generally smaller in size.
Incandescent light bulbs are widely used in household and commercial lighting, for portable lighting, such as table lamps, car headlamps, flashlights, and for decorative and advertising lighting. However, incandescent light bulbs are generally inefficient in terms of energy use and are subject to frequent replacement due to their limited lifetime (about 1,000 hours). Approximately 90% of the energy input is emitted as heat. These lamps are gradually being replaced by other, more efficient types of electric light such as fluorescent lamps, high-intensity discharge lamps, light emitting diodes (LEDs), etc. For the same energy input, these technologies give more visible light and generate much less heat. Particularly, LEDs consume a fraction of the energy used to illuminate incandescent bulbs and have a much longer lifetime (e.g. 50,000 to 75,000 hours). Furthermore, LED light sources are a very clean “green” light source and also provide good color reproduction.
However, a drawback of LED light bulbs is that they have a very limited tolerance to high temperature and their efficiency falls as the temperature rises. The LED devices cannot be operated at the temperature of an incandescent filament (rather, the operating temperature should be around room temperature). The lower operating temperature also reduces the effectiveness of radiative cooling. Current LED lamps have trouble with heat dissipation, since the heat exchange occurs in an enclosed volume. LEDs are not incorporated as part of the outer bulb; therefore, their housing had to be used as a heat sink. In a usual approach, the base of the LED replacement lamp included (in addition to the Edison base connector and the electronics) a relatively large mass of heat sinking material positioned such that it was contacting or otherwise in good thermal contact with the LED device(s).
Another issue is that unlike an incandescent filament, an LED chip or other solid state lighting device typically cannot be operated efficiently using standard 120V or 230V A.C. power. Rather, on-board electronics are typically provided to convert the A.C. input power to D.C. power of lower voltage amenable for driving the LED chips. As an alternative, a series string of LED chips of sufficient number can be directly operated at 120V or 230V, and parallel arrangements of such strings with suitable polarity control (e.g., Zener diodes) can be operated at 120V or 230V A.C. power, albeit at substantially reduced power efficiency. In either case, the electronics constitute additional components of the lamp base as compared with the simple Edison base used in integral incandescent or halogen lamps.
Accordingly, it is desirable to provide an LED light bulb with improved heat management and electronics that may be used as a replacement for a typical incandescent light bulb.